Fe-based sintered alloy

ABSTRACT

There is here disclosed an Fe-based sintered alloy produced through a mixing step of mixing an Fe—Mn alloy powder, graphite powder and Fe powder by a mixer (S 16 ), a compacting step of compacting the mixed powder at a predetermined pressure (S 18 ), and a sintering step of sintering the resultant compact in a sintering oven at a predetermined temperature for a predetermined time (S 20 ), the Fe—Mn alloy powder being characterized by containing 2-30 mass % of Mn. In particular, the mixing step (S 16 ) is carried out by mixing 5-50 mass % of the Fe—Mn alloy powder, 0.2-2 mass % of the graphite powder, and the remainder of the Fe powder in the mixer. Consequently, mechanical strength of the Fe-based sintered alloy can be further improved.

TECHNICAL FIELD

The present invention relates to an Fe-based sintered alloy, and moreparticularly, it relates to an Fe-based sintered alloy produced througha mixing step of mixing an Fe—Mn alloy powder, graphite powder and Fepowder, a compacting step of compacting the mixed powder, and asintering step of sintering the resultant compact.

BACKGROUND ART

A powder metallurgical technique has advantages that size control andcompacting of a complex shape are easier and a cost is lower comparedwith parts producing techniques of casting, forging and the like.Therefore, the powder metallurgical technique is widely used.Particularly in sintered structure parts for automobiles, many Fe-basedsintered alloys are used.

Among the Fe-based sintered alloys, Fe—Cu-based sintered alloys eachproduced by mixing an Fe powder, Cu power and graphite, followed bycompacting and sintering, have heretofore been used. Here, the Cu powderis melted at a sintering temperature or less of the Fe powder to promotethe sintering with the Fe powder, whereby mechanical strength of thesintered alloy is effectively improved. A sintering temperature of theFe—Cu-based sintered alloys is usually in a range of 1100° C. to 1200°C. The Fe—Cu-based sintered alloys are applied to, for example, clutchhubs, connecting rods and the like for automobiles.

Furthermore, in the Fe-based sintered alloy, the improvement of themechanical strength has been made by adding any of various metallicpowders and alloy powders. For example, in an Fe—Mn—Si-based sinteredalloy produced by mixing an Fe—Mn—Si alloy powder including Mn and Si inplace of the Cu powder with the Fe powder and graphite powder,compacting and then sintering the resultant mixture, the mechanicalstrength has been further improved. The above Fe—Mn—Si-based sinteredalloy is principally sintered at 1200° C. or more to promote thesintering of the Fe—Mn—Si alloy powder and the Fe powder, because aliquid phase line of the Fe—Mn—Si alloy powder is at substantially 1200°C. (e.g., see Non-patent Literature 1).

Non-patent Literature 1: Zongyin Zhang and another, Fe—Mn—Si masteralloy steel by powder metallurgy processing, Sweden, Journal of Alloysand Compounds, 2004, Vol. 363, p. 194-202.

DISCLOSURE OF THE INVENTION

To lighten the weight of sintered structure parts for automobiles at alow cost, it is necessary to further improve mechanical strength of theparts at a sintering temperature equal to that of an Fe—Cu-basedsintered alloy in the above conventional technique. Furthermore, in acase where an Fe—Mn—Si alloy powder is used in place of a Cu powder andsintered at the same sintering temperature as that of the Fe—Cu-basedsintered alloy, during the sintering of the Fe—Mn—Si alloy powder and anFe powder, the dispersion of an element such as Mn between the powdersmight be disturbed by an oxide film of Si in the alloy powder formed onthe surface of the alloy powder. In consequence, the sintering cannot bepromoted any more in some cases. Moreover, owing to the addition of Si,an intermetallic compound of Fe and Si is formed in the Fe—Mn—Si alloypowder, and hence the alloy power becomes hard. In consequence, thedensity of a compact decreases, whereby the density of the sinteredalloy also decreases, and hence sufficient mechanical strength cannot beobtained in some cases.

Accordingly, an object of the present invention is to provide anFe-based sintered alloy having improved mechanical strength producedthrough a mixing step of mixing an Fe—Mn alloy powder, graphite powderand Fe powder, a compacting step of compacting the mixed powder, and asintering step of sintering the resultant compact.

The Fe-based sintered alloy according to the present invention is anFe-based sintered alloy produced through a mixing step of mixing anFe—Mn alloy powder, graphite powder and Fe powder, a compacting step ofcompacting the mixed powder, and a sintering step of sintering theresultant compact, and the Fe—Mn alloy powder is characterized bycontaining Mn in an amount of 2-30 mass %.

In the production of the Fe-based sintered alloy according to thepresent invention, the mixing step is preferably accomplished by mixing5-50 mass % of Fe—Mn alloy powder, 0.2-2 mass % of the graphite powderand the remainder of the Fe powder.

As understood from the above, in the production of the Fe-based sinteredalloy according to the present invention, the Fe—Mn alloy powder is usedin place of the Cu powder, and hence the mechanical strength can beimproved at the same sintering temperature as that of the Fe—Cu-basedsintered alloy of a conventional technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing production steps of an Fe-based sinteredalloy, in an embodiment according to the present invention;

FIG. 2 is a diagram showing composition ratios of Mn and the like ofFe—Mn alloy powders produced in Examples A to D, Fe—Mn alloy powders inComparative Examples E and F, an Fe—Mn alloy powder in Example G, andFe—Mn—Si alloy powders in Comparative Examples H to J, in embodimentsaccording to the present invention;

FIG. 3 is a diagram showing material powder mixing ratios and the likeof Fe-based sintered alloys in Examples 1 to 4, Fe-based sintered alloysin Comparative Examples 5 to 7, an Fe-based sintered alloy in Example 8,and Fe-based sintered alloys in Comparative Examples 9 to 16, inembodiments of the present invention;

FIG. 4 is a diagram showing a shape of a compact which is compacted in acompacting step, in the embodiment according to the present invention;

FIG. 5 is a microgram showing a metallic texture of the Fe-basedsintered alloy in Example 2, in the embodiment according to the presentinvention;

FIG. 6 is a diagram showing tensile strengths and the like in caseswhere a plurality of conditions such as compacting conditions andsintering conditions are set in Fe-based sintered alloys in Examples 17to 25, in the embodiments according to the present invention;

FIG. 7 is a diagram showing contents of Mn and the like contained inFe-based sintered alloys in Examples 26 to 31, in the embodimentsaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail withreference to the drawings. FIG. 1 is a diagram showing production stepsof an Fe-based sintered alloy. The Fe-based sintered alloy is producedby a step (S10) of producing an Fe—Mn alloy powder containing Mn in anamount of 2-30 mass %, a step (S12) of producing a graphite powder, astep (S14) of producing an Fe powder, a mixing step (S16) of mixingthese powders, a compacting step (S18) of compacting the mixed powder,and a sintering step (S20) of sintering the resultant compact.

First, the step (S10) of producing the Fe—Mn alloy powder will bedescribed.

The Fe—Mn alloy powder is produced by a gas atomization process so as toobtain the powder having less oxide contents. Needless to say, theproduction of the Fe—Mn alloy powder may be made by use of a mechanicalproduction process such as pulverization, a production process byelectrolysis, a chemical production process by reduction of an oxide orthermal decomposition, or a water atomization process for producing thepowder from a molten metal by jet.

Here, Mn contained in the Fe—Mn alloy powder plays a role of promotingthe sintering between the Fe—Mn alloy powder and the Fe powder by thediffusion of Mn during the sintering. The reason why the content of Mnin the Fe—Mn alloy powder is 2 mass % or more is that if the content ofMn is less than 2 mass %, the diffusion promotion of Mn is poor. Thereason why the content of Mn is 30 mass % or less is that if the contentof Mn is more than 30 mass %, compactibility of the powder in thecompacting step (S18) deteriorates and mechanical strength of a sinteredalloy cannot be improved. Therefore, the Fe—Mn alloy powder containingMn in an amount of 2-30 mass % is used.

As the Fe—Mn alloy powder, there is used a powder passed through a sievehaving a predetermined mesh to regulate particle diameters. If the Fe—Mnalloy powder has large particle diameters, a filling ratio of the powderis low during the compacting of the Fe—Mn alloy powder by the compactingstep (S18), which has an influence on the mechanical strength of thesintered alloy. The Fe—Mn alloy powder having particle diameters of, forexample, 5-50 μm is used. Needless to say, the particle diameters of theFe—Mn alloy powder may be 5-200 μm or 5-100 μm, and these particlediameters are not particularly limited.

Next, the production step (S12, S14) of producing the graphite powderand Fe powder will be described. The graphite powder is produced by amechanical production process such as pulverization and then it is used.Needless to say, the graphite powder may be produced by a chemicalproduction process such as thermal decomposition and then it may beused. Furthermore, the Fe powder is produced by a water atomizationprocess and then it is used. Needless to say, it may be produced by amechanical production process such as pulverization, a gas atomizationprocess, or a reduction process.

The mixing step (S16) of mixing the Fe—Mn alloy powder, the graphitepowder and the Fe powder will be described. A mixed powder is obtainedby mixing 5-50 mass % of the Fe—Mn alloy powder, 0.2-2 mass % of thegraphite powder and the remainder of the Fe powder, and the resultantmixed powder is then used.

The Fe—Mn alloy powder is added to promote the diffusion of elementsbetween the powders during the sintering. The reason why an amount ofthe Fe—Mn alloy powder is 5 mass % or more is that if a mixing ratio ofthe Fe—Mn alloy powder is less than 5 mass %, the promotion of the Mndiffusion is poor, with the result that the mechanical strength of thesintered alloy is not sufficiently improved. The reason why a mixingratio of the Fe—Mn alloy powder is 50 mass % or less is that if themixing ratio of the Fe—Mn alloy powder is more than 50 mass %, thecompactibility of the powder in the compacting step (S18) deterioratesand the mechanical strength of the sintered alloy cannot be improved. Inconsequence, the Fe—Mn alloy powder is used in a mixing ratio of 5-50mass %.

The graphite powder is added to reinforce the Fe-based sintered alloy.The reason why a mixing ratio of the graphite powder is 0.2 mass % ormore is that if it is less than 0.2 mass %, a ferrite increases andhence hardness of the sintered alloy deteriorates, which leads to thedeterioration of the mechanical strength. The reason why a mixing ratioof the graphite powder is 2 mass % or less is that if it is more than 2mass %, a cementite increases and hence toughness of the sintered alloydeteriorates. Therefore, the graphite powder is used in a mixing ratioof 0.2-2 mass %.

In the mixing step (S16), the Fe—Mn alloy powder, graphite powder and Fepowder are sufficiently dried, and these powers are then put into amixer, followed by mixing. It is to be noted that a lubricant may beadded thereto for the purpose of decreasing friction between a mold andthe mixed powder in the subsequent compacting step (S18). As thelubricant, a stearate such as zinc stearate is used. Needless to say,the stearate is not limited, and another type of lubricant may be used.As the mixer for mixing these powders, a V-type mixer may be used, butthis is not particularly limited.

Next, the compacting step (S18) of compacting the mixed powder of theFe—Mn alloy powder, graphite powder and Fe powder will be described. Toimpart a predetermined shape to the mixed powder, for example, a mold ispacked with the mixed powder. The mold packed with the mixed powder ispressed in a monaxial direction to compact it. Needless to say, thepress direction is limited to the monaxial direction, and the mixedpowder may be pressed in an isostatic direction. As a pressure tocompact the mixed powder, 800 Mpa is used. Needless to say, the pressuremay be in a range of 500 MPa to 1500 MPa, but these pressures are notparticularly limited.

As a compacting device, a pressing machine or the like is used in a casewhere the mixed powder is pressed in the monaxial direction. It is to benoted that in a case where the mixed powder is pressed in the isostaticdirection, there is used a CIP (cold isostatic pressing) device, an HIP(hot isostatic pressing) device, or the like. Needless to say, anycompacting machine may be used as long as it can apply the abovepressure, and hence the aforesaid devices are not limited. The mixedpowder is compacted at room temperature, but this temperature is notlimited, and the mixed powder may be compacted while being heated.

Next, the sintering step (S20) of sintering the resultant compact willbe described. The compact obtained by compacting the mixed powder isreleased from the mold, and then sintered in a sintering furnace. For anatmosphere in the sintering furnace, an inert gas, for example, an argongas or a helium gas is used. Needless to say, the sintering atmosphereis not particularly limited, and a decomposed gas of ammonia, hydrogen,or a nitrogen gas may be used. A vacuum atmosphere may also be used.

As a sintering temperature, for example, 1150° C. is used. Needless tosay, the sintering temperature may be in a range of 1100° C. to 1250° C.These sintering temperatures are not particularly limited. As asintering time, for example, a time of 30 minutes is used. Needless tosay, the sintering time may be in a range of 10 minutes to 120 minutes,and these times are not particularly limited. As the sintering furnaceused in the sintering step (S20), a general sintering furnace for use inpowder metallurgy can be used. The sintering furnace is not particularlylimited, so long as it can adjust the above sintering atmosphere,sintering temperature and sintering time.

As will be understood from the above, according to the Fe-based sinteredalloy, Mn in the Fe—Mn alloy powder diffuses in the Fe powder to promotethe sintering, so that the mechanical strength of the Fe-based sinteredalloy can be further improved. Accordingly, sintered structure parts forautomobiles can be lightened at a low cost.

EXAMPLE 1

FIG. 2 is a diagram showing composition ratios of Mn and the like ofFe—Mn alloy powders produced in Examples A to D, Fe—Mn alloy powders inComparative Examples E and F, an Fe—Mn alloy powder in Example G, andFe—Mn—Si alloy powders in Comparative Examples H to J. The alloy powdersin Examples A to D, the Fe—Mn alloy powder in Example G, and the alloypowders in Comparative Examples E and F were produced by a gasatomization process using an inert gas. Furthermore, the alloy powder inComparative Example H was produced by a gas atomization process using aninert gas, the alloy powder in Comparative Example I was produced by apulverization process, and the alloy powder in Comparative Example J wasproduced by a water atomization.

In the alloy powders in Examples A to D, contents of Mn were 2.5 mass %,6 mass %, 18 mass % and 28 mass %, respectively. The alloy powders inExamples A to D were Fe—Mn alloy powders containing 2-30 mass % of Mn.In the alloy powders in Comparative Examples E and F, contents of Mnwere 1.5 mass % and 40 mass %, respectively. The alloy powders producedin Examples A to D and the alloy powders in Comparative Examples E and Fwere classified through a sieve of 330 mesh, and particle diameters ofthe Fe—Mn alloy powders were adjusted to 50 μm or less.

In the alloy powder in Example G, a content of Mn was 6 mass %. Theparticle diameter of the alloy powder in Example G was 100 μm or more,which was larger than that of the other alloy powders.

The alloy powders in Comparative Examples H to J were produced forcomparison with the Fe—Mn alloy powders. In each of the alloy powders inComparative Examples H to J, a content of Mn was 6 mass %, which was thesame as that of Mn in the alloy powder in Example B. Furthermore, eachof the alloy powders in Comparative Examples H to J contained 2 mass %of Si. For the alloy powders in Comparative Examples H to J, theproduction processes thereof were different from each other as describedabove, and hence contents of oxygen contained in the alloy powders weredifferent. The content of oxygen in the alloy powder in ComparativeExample H was 0.06 mass %, and compared with an oxygen content of 0.2mass % in the alloy powders in Comparative Examples I to J, the alloypowder in Comparative Example H produced by the gas atomization processhad the smallest oxygen content. The alloy powders in ComparativeExamples H to J were classified through a sieve of 330 mesh, and aparticle diameter of each alloy powder was adjusted to 50 μm or less.

FIG. 3 is a diagram showing material powder mixing ratios and the likeof Fe-based sintered alloys in Examples 1 to 4, Fe-based sintered alloysin Comparative Examples 5 to 7, an Fe-based sintered alloy in Example 8,and Fe-based sintered alloys in Comparative Examples 9 to 16.

In the Fe-based sintered alloys in Examples 1 to 4, a mixing ratio ofthe alloy powder in Example A was 45 mass %, a mixing ratio of the alloypowder in Example B was 30 mass %, a mixing ratio of the alloy powder inExample C was 10 mass %, and a mixing ratio of the alloy powder inExample D was 6 mass %, respectively. Mixing ratios of the Fe—Mn alloypowders in the Fe-based sintered alloys in Examples 1 to 4 were all in arange of 5 mass % to 50 mass %.

In the Fe-based sintered alloys in Comparative Examples 5 and 6, mixingratios of the alloy powder in Comparative Example E were 60 mass % and99 mass %, respectively. In the Fe-based sintered alloy in ComparativeExample 7, a mixing ratio of the alloy powder in Comparative Example Fwas 2 mass %. In the Fe-based sintered alloy in Example 8, a mixingratio of the alloy powder in Comparative Example G was 3 mass %.

Furthermore, in every case of the Fe-based sintered alloys in Examples 1to 4, the Fe-based sintered alloys in Comparative Examples 5 to 7, andthe Fe-based sintered alloy in Example 8, a mixing ratio of the graphitepowder was 1 mass %, which was in a range of 0.2 mass % to 2 mass %.

In each of the Fe-based sintered alloys in Comparative Examples 9 to 11,a mixing ratio of the alloy powders in Comparative Examples H to J was30 mass %, and a mixing ratio of the graphite powder was 1 mass %.

In each of the Fe-based sintered alloys in Comparative Examples 12 to13, a mixing ratio of the alloy powder in Example B was 30 mass %.Furthermore, in the Fe-based sintered alloy in Comparative Example 12, amixing ratio of the graphite powder was 0.1 mass %, and in the Fe-basedsintered alloy in Comparative Example 13, a mixing ratio of the graphitepowder was 2.5 mass %.

In the Fe-based sintered alloy in Comparative Example 14, a mixing ratioof the alloy powder in Example A was 55 mass %, and in the Fe-basedsintered alloy in Comparative Example 15, a mixing ratio of the alloypowder in Example D was 3 mass %. In every case of the Fe-based sinteredalloys in Comparative Examples 14 and 15, a mixing ratio of the graphitepowder was 1 mass %. It is to be noted that the Fe-based sintered alloyin Comparative Example 16 was a conventional Fe-based sintered alloywhich was mixed with a Cu powder stipulated in JIS S MF4050.

For the production of the Fe-based sintered alloy shown in FIG. 3,material powders of each Fe-based sintered alloy were mixed in a mixingratio shown in FIG. 3 in the above mixing step (S16). Prior to themixing, 0.8 mass % of zinc stearate was added as a lubricant to thematerial powders, and the mixing was carried out by use of a V-typemixer.

The mixed powder obtained by the mixing in the mixing step (S16) wascompacted in the above compacting step (S18). The compacting was carriedout by putting the mixed powder into the mold, and then pressing it at800 MPa in a monaxial direction by a pressing machine. FIG. 4 is adiagram showing a shape of a compact which was compacted in thecompacting step (S18).

The compact obtained in the compacting step (S18) was sintered in theabove sintering step (S20). The sintering was carried out at a sinteringtemperature of 1150° C. for a sintering time of 30 minutes in a nitrogengas atmosphere by use of a sintering furnace. For the Fe-based sinteredalloys shown in FIG. 3, tensile tests were carried out at roomtemperature in accordance with JIS Z 2241. A shape of each test piecefor the tensile test was the same as shown in FIG. 4. Furthermore, atensile test speed was 0.5 mm/minute in terms of a cross head speed of atensile tester.

According to the results of the tensile tests, as shown in FIG. 3, theFe-based sintered alloys obtained in Examples 1 to 4 had tensilestrengths of 620-650 MPa. It is shown that all the Fe-based sinteredalloys were more improved in tensile strength than the conventionalFe-based sintered alloy in Comparative Example 16. Furthermore, theFe-based sintered alloys in Examples 1 to 4 had higher tensile strengthsthan the other Fe-based sintered alloys shown in FIG. 3, andparticularly in the Fe-based sintered alloys in Examples 1 to 4, highertensile strengths were obtained than the Fe-based sintered alloys usingFe—Mn—Si alloy powders in Comparative Examples 9 to 11.

For the Fe-based sintered alloys shown in FIG. 3, density measuringtests were carried out in accordance with JIS Z 2501. The shape of atest piece for each density measuring test was the same as shown in FIG.4. According to the results of the density measuring tests, as shown inFIG. 3, the Fe-based sintered alloys obtained in Examples 1 to 4 haddensities of 7.15-7.25 g/cm³. As will be understood from the above, inthe Fe-based sintered alloys in Examples 1 to 4, higher densities wereobtained than the other Fe-based sintered alloys shown in FIG. 3.

To examine a diffusion state of Mn from the Fe—Mn alloy powder into theFe powder, a concentration of Mn at a site formed from the Fe powder wasanalyzed using electron probe micro-analysis (EPMA). As an example, FIG.5 is a microgram showing a metallic texture of the Fe-based sinteredalloy in Example 2. As an analyzer, an X-ray microanalysis device (type:MACHS200, made by Shimadzu Seisakusho Ltd.) was used. In the Fe-basedsintered alloys in Examples 1 to 4, the concentrations of Mn at the siteformed from the Fe powder were in a range of 1 mass % to 2 mass %. Inthe Fe-based sintered alloys in Examples 1 to 4, the concentrations ofMn at the site formed from the Fe powder were higher than the otherFe-based sintered alloys shown in FIG. 3, and it is shown that Mn wasdiffused in large quantities from the Fe—Mn alloy powder into the Fepowder during the sintering.

FIG. 6 is a diagram showing tensile strengths and the like in a casewhere a plurality of conditions such as compacting conditions andsintering conditions are set in Fe-based sintered alloys in Examples 17to 25. The Fe-based sintered alloys in Examples 17 to 25 were producedby mixing 30 mass % of the alloy powder in Example B, 1 mass % of thegraphite powder and the remainder of the Fe powder in mixing ratios, andsetting a plurality of conditions of a compacting pressure in the abovecompacting step (S18) as well as a sintering temperature and a sinteringtime in the above sintering step (S20).

The Fe-based sintered alloys in Examples 17 to 19 were produced settingcompacting pressures to 300 MPa, 500 MPa and 1500 MPa while a sinteringtemperature of 1150° C. and a sintering time of 30 minutes were fixed.The Fe-based sintered alloys in Examples 20 to 22 were produced settingsintering temperatures to 1050° C., 1100° C. and 1250° C. while acompacting pressure of 800 MPa and a sintering time of 30 minutes werefixed. The Fe-based sintered alloys in Examples 23 to 25 were producedsetting sintering times to 5 minutes, 10 minutes and 120 minutes while acompacting pressure of 800 MPa and a sintering temperature of 1150° C.were fixed.

For the Fe-based sintered alloys in Examples 17 to 25, tensile tests anddensity measuring tests were carried out in the above test manners. Asshown in FIG. 6, the Fe-based sintered alloys having tensile strengthsof 600 MPa or more were obtained by compacting under compactingpressures of 500-1500 MPa, and then sintering at sintering temperaturesof 1100° C.-1250° C. for sintering times of 10-120 minutes. Furthermore,the Fe-based sintered alloys having tensile strengths of 600 MPa or morehad densities of 7.2-7.4 g/cm³.

FIG. 7 is a diagram showing contents of Mn and the like contained inFe-based sintered alloys in Examples 26 to 31. The Fe-based sinteredalloys in Examples 26 and 29 were Fe-based sintered alloys including thealloy powder in Example A in mixing ratios of 30 mass % and 15 mass %,respectively. The Fe-based sintered alloys in Examples 27 and 30 wereFe-based sintered alloys including the alloy powder in Example C inmixing ratios of 25 mass % and 35 mass %, respectively. The Fe-basedsintered alloys in Examples 28 and 31 were Fe-based sintered alloysincluding the alloy powder in Example D in mixing ratios of 15 mass %and 25 mass %, respectively. Furthermore, each of the Fe-based sinteredalloys in Examples 26 to 31 included the graphite powder in a mixingratio of 1 mass %.

Each of the Fe-based sintered alloys in Examples 26 to 31 was producedby mixing material powders in a material powder mixing ratio shown inFIG. 7 in the above mixing step (S16), pressing and compacting the mixedpowder at 800 MPa in the above mixing step (S18), and then sintering theresultant compact at a sintering temperature of 1150° C. for a sinteringtime of 30 minutes in the above mixing step (S20).

For the Fe-based sintered alloys in Examples 17 and 25, tensile tests,density measuring tests and concentration analyses of Mn at a siteformed from the Fe powder were carried out in the above manners. Acontent of Mn in each Fe-based sintered alloy was measured andcalculated using a high-frequency plasma atomic emission spectrometer(ICP).

As shown in FIG. 7, in the Fe-based sintered alloys in Examples 26 to28, contents of Mn were 0.8 mass %, 4.5 mass % and 4.2 mass %,respectively. In the Fe-based sintered alloys in Examples 29 to 31,contents of Mn were 0.4 mass %, 6.3 mass % and 7.0 mass %, respectively.In every case of the Fe-based sintered alloys in Examples 26 to 28,tensile strengths were 600 MPa or more. Therefore, the content of Mn inthe Fe-based sintered alloy which can obtain a tensile strength of 600MPa or more was 0.5-5 mass %.

1. An Fe-based sintered alloy produced through a mixing step of mixingan Fe—Mn alloy powder, graphite powder and Fe powder, a compacting stepof compacting the mixed powder, and a sintering step of sintering theresultant compact, the Fe—Mn alloy powder being characterized bycontaining 2-30 mass % of Mn.
 2. The Fe-based sintered alloy accordingto claim 1, wherein the mixing step is characterized by mixing 5-50 mass% of the Fe—Mn alloy powder, 0.2-2 mass % of the graphite powder, andthe remainder of the Fe powder.